Reassigning channels in a spatial diversity radio communications system

ABSTRACT

Methods and systems are provided for assigning channels in a spatial division multiple access communication network. The network includes a plurality of conventional channels some of which are configurable to be shared concurrently by plural subscribers. The method includes determining combinations of subscribers from the existing subscribers. Enhancement activities are invoked to create optimal combinations of existing subscribers. Existing subscribers are reassigned as necessary to share channels thereby freeing resources for new subscribers.

This application is a continuation of U.S. patent application Ser. No.09/967,882, filed on Sep. 28, 2001, and entitled “Channel Assignments ina Wireless Communication System Having Spatial Channels IncludingEnhancements in Anticipation of New Subscriber Requests”, the priorityof which is hereby claimed.

The present invention relates generally to wireless communicationsystems.

BACKGROUND OF THE INVENTION

Wireless communication systems are generally allocated a portion of theradio frequency (RF) spectrum for their operation. The allocated portionof the spectrum is divided into communication channels and channels aredistinguished by frequency, time or code assignments, or by somecombination of these assignments. Each of these communication channelswill be referred to as conventional channels, and a conventional channeltypically corresponds to a full-duplex channel unless otherwise noted.The establishment of a communication link in a communication systemdepends not only on the availability of a conventional channel but alsoon the quality of communication that will result from the use of a givenavailable conventional channel.

In wireless communication systems, a conventional channel is used forcommunication between a base station (sometimes referred to as cellstation) and a subscriber station (sometimes referred to as a personalstation). A cell station provides coverage to a geographic area referredto as a cell and may be a point-of presence providing a connectionbetween the subscriber station and a wide area network such as a PublicSwitched Telephone Network (PSTN). The underlying motivation for the useof cells in wireless systems is the ability to reuse a particularportion of the RF spectrum available in geographically different areas.The reuse of the frequency spectrum can introduce co-channel (intercell)interference between users in different cells that share a commonconventional channel. If co-channel interference is not carefullycontrolled, it can severely degrade the quality of communications.System capacity is in general limited by interference because of thereduction in number of reusable channels of acceptable quality.

Each cell is organized about a cell station. The cell station includesmultiplexing equipment for accepting incoming telephone landlines (i.e.,voice or data lines) and multiplexing the incoming voice/data signalsonto a radio frequency (RF) carrier that is broadcast by an antennasystem over a region that the cell is designated to cover. Individualsubscriber stations (e.g., handsets and the like) are each equipped toreceive the broadcast modulated carrier and to demultiplex aspecifically assigned channel of the carrier that carries the voice/datathat is intended for a given receiver.

In a conventional wireless communication system, an assigned RFbandwidth of frequencies is simultaneously shared by multiplesubscribers. Three techniques for sharing bandwidth are frequencydivision multiple access (FDMA), time division multiple access (TDMA)and code division multiple access (CDMA). In FDMA systems, the availablebandwidth is sub-divided into a number of sub-bands. Each sub-bandaccommodates a carrier that is modulated by a subscriber's data. In TDMAsystems, time-sharing is used to multiplex multiple subscribers. Eachsubscriber is allocated a periodic time-slot for transmission of data.In CDMA systems, multiple subscribers are accommodated on a singlecarrier (or sub-carrier) and each subscriber is assigned a code waveformthat is used to modulate the carrier for each bit of data beingtransmitted. Each subscriber has an assigned coded waveform taken from aset of orthogonal waveforms, thus allowing the system to separate(demodulate) the individual subscriber transmissions.

Cellular communication systems may also use spatial division multipleaccess (SDMA) techniques for providing increased subscriber systemcapacity in systems that use FDMA, TDMA, and/or CDMA methods without anyincrease in the allocated RF bandwidth. SDMA techniques are discussed ingreater detail in U.S. Pat. No. 5,515,378, to Roy III, et. al., entitled“Spatial Division Multiple Access Wireless Communication Systems.” SDMAexploits the spatial distribution of subscribers in order to increasethe usable system capacity. Because subscribers tend to be distributedover a cell area, each subscriber-cell station pair will tend to have aunique spatial signature characterizing how the cell station antennaarray receives signals from the subscriber station, and a second spatialsignature characterizing how the cell station antenna array transmitssignals to the subscriber station. Subscribers sharing the sameconventional channel on a unique basestation are said to be usingdifferent spatial channels. The necessary data (referred to as thespatial signature of a subscriber) for implementing SDMA is obtainedempirically from the transmissions received by the cell station fromeach active subscriber. Where spatial signatures are used, the effectiveradiation patterns of the antenna array can allow more than onesubscriber to use a given packet time-slot, code or frequency. Forexample, if the effective radiation pattern of a first subscriberresults in a relatively low energy “null” in the vicinity of a secondsubscriber sharing a packet time allocation, and the second subscriber'sspatial signature results in a null in the vicinity of the firstsubscriber, the simultaneous RF packet transmissions will not causeinterference upon reception at the two subscriber stations. Also,transmissions from the two subscribers to the cell station will beseparable at the cell station.

A conventional wireless communication system includes a finite number ofchannels on which signals are transmitted. The number of channelsdepends on many system factors. By sharing a channel among subscribers,as discussed above with respect to SDMA techniques, more subscribers canbe accommodated.

A particular example of an existing protocol for establishing aconnection in a cellular communication system between a subscriberstation and the cell station is described in “Personal Handy PhoneSystem” which is part of the Association of Radio Industries andBusinesses (ARIB) Preliminary Standard, Version 2, RCR STD-28, approvedby the Standard Assembly Meeting of December, 1995.

In accordance with the PHPS standard, a control sequence is used toset-up and establish an incoming call to a subscriber station (i.e., apersonal station or PS). The sequence includes:(1) the CS paging on apaging channel (PCH) of the selected PS to which an incoming connectionis desired;(2) the selected PS responding on the signaling controlchannel (SCCH) by sending a link channel establishment request;(3) theCS responding to the PS request by selecting a traffic channel (TCH) andsending the selected TCH as a link channel (LCH) assignment to the PS onthe SCCH; (4) the selected PS switching to the assigned LCH andtransmitting a sequence of synchronization (SYNC) burst signals followedby a sequence of idle traffic bursts; and (5) upon successful detectionof a synchronization signal, the CS responds by transmitting a sequenceof SYNC bursts on the LCH followed by a sequence of idle traffic burstsand then proceeding to establish a connection with the incoming call tothe CS, invoking any additional optional signaling that may be required(e.g. encryption and user authentication).

The control sequence for establishing an uplink connection initiated bya PS desiring to connect to the CS includes:(1) the PS sending a linkchannel establishment request on the signaling control channel (SCCH);(2) the CS responding to the PS request by selecting a traffic channel(TCH) and sending the selected TCH as a link channel (LCH) assignment tothe PS on the SCCH; (3) the PS switching to the assigned LCH andtransmitting a sequence of synchronization (SYNC) burst signals followedby a sequence of idle traffic bursts; and (4) upon successful detectionof the synchronization signal, the CS responds by transmitting asequence of SYNC bursts on the LCH followed by a sequence of idletraffic bursts and then proceeding to establish a connection with theincoming call to the CS, and invoking any additional optional protocolsthat may be required (e.g. encryption and user authentication).

In systems that use SDMA techniques, the control sequences describedabove can be modified depending on the number of subscribers beingserviced and the number of channels available. For example, if aconnection is sought to add a subscriber when there are no availablechannels (i.e., all available channels are assigned to subscribers), thesequence may be augmented to include a channel sharing selectionprocess. One example of a channel sharing selection process is describedin the commonly owned U.S. Pat. No. 5,886,988, entitled “CHANNELASSIGNMENT AND CALL ADMISSION CONTROL FOR SPATIAL DIVISION MULTIPLEACCESS COMMUNICATION SYSTEMS,” the contents of which are expresslyincorporated herein by reference. When a new subscriber is added, asharing decision is made as to which current subscriber is the bestmatch for pairing with the new subscriber. The sequence includes anassignment of the new subscriber to the channel occupied by the selectedcurrent subscriber, forming a best match.

While spatial channels can be used to increase the traffic managed percell station, the use of spatial channels also increases the risk ofcall quality degradation and even call drop. Conventional systems assignnew users or existing users locations for transmission consisting of atime slot and a frequency. Every transmission location has a risk ofinterference associated with it. Conventional systems manage these risksby monitoring various combinations of time slots and frequency toevaluate which location poses the least risk of interference to both thebasestation and the phone. If the basestation incorrectly evaluates riskit might assign a call to a location that has a high level ofinterference causing performance problems or call drop. Basestationscurrently move calls around to different locations but only when thecall quality starts to suffer.

When SDMA techniques are used, making a best pairing decision becomesparamount to performance. If not careful, a new subscriber may beassigned to a cell station and a channel on which poor quality isexperienced due to excessive interference from the signal transmitted toa co-user. Moreover, the addition of a new subscriber has the potentialconsequence of adversely affecting the quality of communications onexisting connections. Existing subscribers can suffer from increasedchannel interference from the addition of a new subscriber, or otherunrelated causes, that can require moving subscribers from currentlyassigned channels to new channels in order to restore acceptable qualitycommunications.

As described above, the spatial signature data collected forimplementing SDMA and making the pairing decisions is obtainedempirically from the transmissions received by the cell station fromeach active subscriber, including the new subscriber. However, thetransmissions from the new subscriber necessarily are limited in nature(i.e., the new subscriber has been connected to the CS for only a smallamount of time) and, as such, selections based on this limited amount ofdata may be less than optimal. The transmission characteristics ofexisting subscribers tend to be easier to quantify due to the length oftime the connections have been set up. Further, some calls may be soshort lived that the pairing of a new subscriber with the short callsubscriber may be not desirable.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a method for assigning channels ina spatial division multiple access communication network. The networkincludes a plurality of conventional channels some of which areconfigurable to be shared concurrently by plural subscribers. Theinvention provides a method for preparing the communication system for anew subscriber. The method includes evaluating combinations of existingsubscribers including rating each combination and storing initial ratinginformation and initiating enhancing activities for one or moresubscribers associated with one or more combinations indicated by therating information where the enhancing activities are operable toimprove a rating for a given combination such that a proposedcombination is better suited for spatial channels than as indicated bythe initial rating information for the combination.

Aspects of the invention can include one or more of the followingfeatures. The method can include reassigning existing subscribers basedon the improved rating information prior to the initiation by the newsubscriber. The reassigning step can include reassigning one or moreexisting subscribers including freeing a conventional channel for use bya prospective new subscriber.

The enhancing activities can include: changing an alignment of one ormore existing subscribers in a combination indicated by the initialrating information to be a best combination; changing an alignment sothat all subscribers in a combination have alignments that match;changing an alignment so that all subscribers to a group are differentby a predetermined amount; determining an optimal alignment forsubscribers that are to share a given spatial channel in thecommunication system and aligning the subscribers in the combination inaccordance with the optimal alignment; or determining if a bestcombination of subscribers does not satisfy a first performance criteriabased on the initial rating information and as such the combination isnot a good candidate for spatial channels, determining if enhancingactivities as applied to members of the best combination would create aspatial channel that satisfies the first performance criteria, and ifnot, applying a different set of enhancing activities to members of thecombination such that a combination of one or more new subscribers andone or more members of the combination will satisfy the firstperformance criteria.

The first performance criteria can be an alignment or frequency criteriafor each subscriber assigned to a spatial channel in the communicationsystem. The first performance criteria can be selected from the groupcomprising, bit error rate, frame error rate, alignment, speed factor,dynamic range factor, correlation factor and relative signal strengthfactor.

The enhancing activities can include changing an alignment of one ormore existing subscribers in a combination; changing an alignment for aplurality of subscribers to form a group of subscribers having anidentical alignment such that a new subscriber having a differentalignment can be paired with one or more of the group to form a spatialchannel; or changing a frequency of one or more existing subscribers ina combination indicated by the initial rating information to be a bestcombination. The reassigning step can include reassigning one or moreexisting subscribers including freeing a conventional channel for use bya prospective new subscriber. The enhancing activities can includeforcing transmit weights for terminal units associated with one or moresubscribers to be orthogonal to a spatial signature of anothersubscriber in a combination.

In another aspect, the invention provides a method for assigningchannels in a spatial division multiple access communication network.The method includes determining a network loading threshold forconventional channels including determining a number of channels to beshared concurrently by plural subscribers and the number subscribers toshare each channel, determining one or more acceptable combinations ofsubscribers from the existing subscribers without violating the networkloading threshold including reducing a number of subscribers assigned toat least one channel and reassigning the existing subscribers asnecessary to form the acceptable combinations creating one or morespatial channels and thereby freeing space on the one channel for afuture subscriber.

The method can include receiving a request to add a new subscriber,determining if the network loading threshold would be exceeded by addingthe new subscriber and, if not, adding the new subscriber to the onechannel.

Aspects of the invention can include one or more of the followingadvantages. A system is provided that continuously monitors existingsubscriber communication channels, evaluating grouping opportunities,and when required to make grouping decisions to support new subscribers,determines a best matching group of subscribers from all of the existingsubscribers including the new subscriber. The system also continuouslymonitors existing subscriber communication channels for grouping orseparation (decoupling) opportunities. The system performs analysis inthe background at regular intervals and stores group rating data in amatrix that can easily be retrieved at a time when grouping decisionsare required to be made. A system is provided to evaluate and managerisk in a wireless communication system. Risk management includes theevaluation of one or more risk criteria including evaluating factorsassociated with interference and each caller. The factors can beselected from spatial signature, signal strength, and other quantities.

These and other advantages will be readily apparent to those of ordinaryskill in the art from the description below, the figures and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless SDMA TD/FD/CDMA system.

FIG. 2 is a flow diagram for a method for channel assignment.

FIG. 3 is a flow diagram for a method for channel assignment thatincludes enhancement activities.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a wireless SDMA TD/FD/CDMA system (wireless system 10) inwhich a number of subscriber stations (symbolically shown as mobileunits) 20, 22, 24 are being served by cell station 100 that may beconnected to a wide area network (WAN) 56 for providing any requireddata services and connections external to the immediate wireless system10. Switching network 58 interfaces with WAN 56 for providingmulti-channel duplex operation with the WAN by switching incoming WANdata to lines 60 of cell station 100 and switching outgoing signals fromcell station 100, on line 54 to the WAN. Incoming lines 60 are appliedto signal modulators 62 that produce modulated signals 64 for eachsubscriber station 20-24 in communication with cell station 100. A setof spatial multiplexing weights 74 for each subscriber station 20-24 areapplied to the respective modulated signals in spatial multiplexers 66to produce spatially multiplexed signals 68 to be transmitted by a bankof multi-channel transmitters 70 using transmit antenna array 18. TheSDMA processor (SDMAP) 48 produces and maintains spatial signatures foreach subscriber station for each conventional channel, calculatesspatial multiplexing and demultiplexing weights for use by spatialmultiplexers 66 and spatial demultiplexers 46, and uses the receivedsignal measurements 44 along with other data to select a channel for anew connection. A process for selecting a channel for a new connectionis described in greater detail below. Accordingly, the signals from thecurrent active subscriber stations, some of which may be active on thesame conventional channel, are separated and interference and noisesuppressed. When communicating from the cell station to the subscriberstations, an optimized multi-lobe antenna radiation pattern tailored tothe current active subscriber station connections and interferencesituation is created.

Spatial demultiplexers 46 combine received signal measurements 44 fromthe multi-channel receivers 42 and associated antenna array 19 accordingto spatial demultiplexing weights 76, a separate set of demultiplexingweights being applied for each subscriber station communicating with thecell station I 00. The outputs of spatial demultiplexers 46 arespatially separated signals 50 for each subscriber station 20-24communicating with the cell station 100, which are applied to signaldemodulators 52 to produce demodulated received signals 54. In oneimplementation, the demultiplexing and demodulation processing areperformed together in a nonlinear multidimensional signal processingunit.

The demodulated received signals 54 are then available to switchingnetwork 58 and WAN 56. In an FDMA system implementation, eachmulti-channel receiver and each multi-channel transmitter is capable ofhandling multiple frequency channels. In other implementations,multi-channel receivers 42 and multi-channel transmitters 70 may insteadhandle multiple time slots, as in a TDMA system; multiple codes, as in aCDMA system, or some combination of these well known multiple accesstechniques. Because of the interference introduced by frequency reuseand the fragile nature of orthogonality for conventional and spatialchannels, the wireless SDMA system 10 includes a method for cell stationand channel assignment that minimizes these adverse effects when a newcall or connection between a cell station and a subscriber is made. Thelabels new subscriber and new connection will be used interchangeably todenote a new call or connection between a cell station and a subscriberstation, and the labels active subscriber, existing connection andexisting subscriber will be used interchangeably to denote a call orconnection in-progress between a cell station and a subscriber station.

Channel assignment in a full-duplex communication channel includes theselection of both an uplink channel (from subscriber to cell station)and a downlink channel (from cell station to subscriber). The case ofhalf-duplex channel assignment may be considered as a special case ofthe full-duplex case. Interference on the uplink channel comes primarilyfrom other subscriber stations while interference on the downlinkchannel is caused primarily by other cell stations. Consequently, thequality of communications on the uplink and downlink channels willgenerally differ. In one implementation of the invention, uplink anddownlink channel assignments are performed independently and separately.However, many practical systems impose a fixed relationship between theuplink and downlink channels so that independent selection is notpossible. For example, in the Personal Handyphone System (PHS) standard,the uplink and downlink channels form a full-duplex channel and must beon the same RF carrier, so that the carrier frequency of the uplink anddownlink channel cannot be independently specified. Also, the downlinktime division multiplexed time-slot is specified as preceding the uplinktime-slot by exactly four time-slots. For such systems, the selection ofeither uplink or downlink channel automatically determines the selectionof the other. Systems and considerations for selecting channels aredescribed in “CHANNEL ASSIGNMENT AND CALL ADMISSION CONTROL FOR SPATIALDIVISION MULTIPLE ACCESS COMMUNICATION SYSTEMS.”

As previously explained, in SDMA there are two or more spatialsignatures associated with each subscriber-base station pair on aparticular conventional channel. Cell station 100 associates with eachsubscriber station a receive, or uplink, spatial signature related tohow that subscriber station receives signals transmitted to it by thebase station's antenna array and a transmit, or downlink, spatialsignature related to how the base station's receive antenna arrayreceives signals transmitted by the subscriber station. The transmit andreceive spatial signatures contain information about the amplitudeattenuation and relative phase of the RF signal at each antenna elementtransmitter and receiver, respectively, of the cell station. Thisamplitude and phase information at each receiver or transmitter can betreated as vector elements of a complex column vector and be stored in adatabase and updated at prescribed intervals. The spatial signatures maybe estimated during the initial phase of a call setup when a newconnection from a subscriber is initiated, or they may be analyticallydetermined. For example, a link channel establishment phase can beinitiated on the signaling control channel (SCCH) before communicatingon an assigned link (traffic) channel (LCH). During this link channelestablishment phase, the spatial signatures of the new subscriber can bemeasured.

Several optional approaches to uplink channel assignment are available,each varying in relative complexity and performance characteristics: aWeighted Correlation method, a Predicted Quality method, and aHierarchical method combining both the Weighted Correlation method andthe Predicted Quality method. Each of these methods is discussed in“CHANNEL ASSIGNMENT AND CALL ADMISSION CONTROL FOR SPATIAL DIVISIONMULTIPLE ACCESS COMMUNICATION SYSTEMS.”

In one implementation, a subscriber's call is assigned to a conventionalchannel with an acceptable cost. Cost functions are described in greaterdetail in “CHANNEL ASSIGNMENT AND CALL ADMISSION CONTROL FOR SPATIALDIVISION MULTIPLE ACCESS COMMUNICATION SYSTEMS.” The cost functions areused to compare pairings between subscribers.

In one implementation, a pairing matrix (spatial matrix) is used tostore the results of the pairing analysis for each potential pair ofsubscribers. Each entry in the matrix corresponds to a recommendationfor a given pairing of subscribers. The spatial matrix can be updated inthe background using received signal data 44 (FIG. 1) and call qualityreports generated by SDMAP 48. In one implementation, the spatial matrixreflects a recommendation for pairing based on an analysis of one ormore of the following characteristics associated with the subscribers toa pair: speed, dynamic range, correlation, frame error rate (FER),received signal strength indicator (RSSI), alignment and longevity(time). In the preferred implementation, the recommendation indicates apairing of existing subscribers that is optimal. Based on therecommended pairing, an existing subscriber is moved and paired withanother existing subscriber, while the new subscriber is assigned to thenow free conventional channel. The process for assigning channels andmonitoring channels for pairing and separation opportunities isdescribed in greater detail below. While the system below will bedescribed in terms of pairs of callers, other groupings of two or morecallers may be made by the system. In these implementations, the spatialmatrix can include entries for each potential grouping.

Call Monitoring

Each call (subscriber) is monitored and call processing is performed toprovide regular updates to the spatial matrix. In one implementation,plural buffers are used to store and process data. In oneimplementation, subscriber data is received at a first buffer untilfull, then written to a second buffer. The first buffer is processedwhile the second buffer is filling so that statistical data can begathered contemporaneously with the collection of new data. The processis reversed when the second buffer becomes full.

In one implementation, histograms are used to store data collected for agiven characteristic. The histograms can include plural bins and can beused to collect data over a fixed length period of time. At the end of atime period, the data can be analyzed and used in computing arecommendation as is described in greater detail below. Alternatively,instead of using fixed length time windows for monitoring caller data,exponentially weighted histograms can be used. At every iteration,entries in a given histogram associated with a given parameter (i.e.,characteristic, such as speed factor) can be multiplied by a fixedfraction (“the weighting”). Thereafter, any newly received data can beadded to the histogram. Exponential weighting can be faster and morestable to implement. Histograms and data collection methods for use inmaking recommendations for combinations of existing subscribers arediscussed in greater detail below.

Speed Factor

The spatial signature for a user on a spatial channel ideally should bestable. Accordingly, highly mobile subscribers are not ideal candidatesfor groupings. In one implementation, the relative speed of a subscriberis calculated using the dot product of the spatial signature of eachpair of consecutive, error free bursts received by the cell station.Each value can in turn be entered into a plural (e.g., 4) bin histogram.In one implementation, the dot products are normalized and filtered suchthat only the 0.5, 2.0, 8.0 and 25.0 percentiles of each time intervalare stored in the histogram. A speed factor for each subscriber is thendefined based on the number of entries in the respective bins of thehistogram. A speed threshold may be set, and compared to the speedfactor. If the speed factor exceeds the threshold, then the individualsubscriber is a poor candidate for grouping. In one implementation, eachcandidate to a pair is evaluated (s_(i) & s_(j)), the results of whichare combined to produce a resultant speed factor for the pairings_(r)=f(s_(i), s_(j)). The resultant speed factor can be used in thecalculation of the recommendation for the pairing that is stored in thespatial matrix.

Dynamic Range Factor

Two signals on a spatial channel call ideally must stay within a certainrange from each other for the algorithms proposed to maintainefficiency. Dynamic range is measured by the difference between thesignal levels of the received signals associated with the subscribers.In one implementation, a received signal strength indicator (RSSI)difference can be calculated between two candidate subscribers at eachgood burst. The results can be stored in a plural bin (e.g. 4)histogram. At an appropriate time, the results can be evaluated and adynamic range factor (DynRange_(ij)) for the pairing assigned based onthe entries in the histogram bins. A threshold can be defined at which apairing is deemed unacceptable. The use of thresholds is discussed ingreater detail below in calculating recommendations to be included inthe spatial matrix.

In one implementation, approximately a 15 dB threshold for separationbetween the subscribers is used. In one implementation, four histogrambins are used each with ranges that spanned from 0 to the thresholdvalue over small dynamic ranges (e.g., 5 dB dynamic range where bin 1(0-5 dB), bin 2 (5-10 dB), bin 3 (10-15 dB) and bin 4 (greater than 15dB)). In this way, pairs of candidate that have differences that aregreater than the threshold can be discarded immediately, while changesin the threshold may be able to be realized without changing the binassignments (e.g., a threshold of 10 dB could be realized by evaluatingthe contents of bins 1 and 2 and disregarding the contents of bins 3 and4).

User Correlation Factor

In one implementation, correlation data describing the degree ofdifference between spatial signatures of a proposed grouping (e.g.,pair) are evaluated. The correlation between the spatial signatures canbe computed on each time interval and accumulated in a plural binhistogram. Again, the bins can be assigned ranges of correlation thatcorrespond to small ranges between little or no correlation (i.e.,decorrelated subscribers) and an unacceptable level of correlation(e.g., a correlation threshold). In one implementation, the correlationfactor (correlationsJ) is computed as a correlation coefficient that isequal to the absolute value of the dot product of the normalized sourcespatial signatures of a burst from one subscriber and another.

Frame Error Rate Factor

Frame error rate (FER) information for a subscriber can be reported tothe SDMAP 48 (FIG. 1) at preset intervals. In one implementation, theFER information is reported every 100 ms. In one implementation, afiltered FER value is stored for each call. The FER can be averaged overa time interval, then a running filtered value can be computed. Therunning filtered value can be used to discard as non-optimal calls thathave an unacceptably high FER as candidates for grouping. In oneimplementation, the filtered FER value is compared to a threshold and aresultant FER factor (FER_(i) and FER_(j)) is determined for eachsubscriber. Alternatively, the FER factor can be derived from ananalysis of histogram data associated with the filtered FER value datacollected for a given subscriber.

Alignment Factor

As described above, in order to successfully share a channel, thespatial receivers must be able to differentiate between signals sent bythe respective paired subscribers. In one implementation, an alignmentfactor (Align_(ij)) is determined for each pairing. Alignment (or lackthereof) is a measure of the systems ability to differentiate two usersby looking for the user's respective unique words. If the alignmentfactor is high or set, then one user's unique word can be identifiedduring one window while the other user's unique word can be identifiedduring another window that is sufficiently (e.g., significantly) shiftedfrom the first. In one implementation, the difference is a predeterminedlarge number that allows the system to differentiate one user fromanother. In another implementation in which the system is oversampled,the alignment of both users must fall on the same sample thus allowingfor faster simultaneous processing of both users.

Time Factor

In one implementation, a minimum time threshold for a call isestablished. A timer measures call duration, and after the threshold hasbeen exceeded, the call (i.e., subscriber) becomes a candidate forgrouping. In one implementation, two thresholds can be established, oneless than the second. The first threshold can be set to a time intervalthat corresponds to a call duration in which the chance for success fora spatial channel is high. The second threshold can be set to a timeinterval that corresponds to a call duration in which the chance forsuccess for a spatial channel is optimal. In one implementation, thetime interval for the second threshold can be set to be approximately 2seconds. Setting the time interval at approximately two seconds mayresult in all registration calls and most regular P-Mail messages beingdiscarded as candidates for sharing. The setting of the time interval isa trade off. Some short duration calls are poor candidates for sharing(i.e., those calls for which the base station did not gather enough datato produce a good recommendation). However, some short duration callsare good candidates for sharing (e.g., location registration or Pmail)because these types of calls can support more quality degradation than aconventional voice call. For example, if a location registration callfails, the handset will try again, and the failure and re-registrationwill not have any consequences for the user. Accordingly, the setting ofthe thresholds will depend on various system factors.

A time factor (t_(ij)) can be set for a prospective pairing using thecomparison results from the call duration and the various thresholds.For example, if both calls have exceeded the optimal threshold, the timefactor (t_(ij)) can have the value of 1. If either call duration is lessthan a minimum time threshold, the time factor (t_(ij)) can be set to avalue of 0. Other time factor (t_(ij)) values, between 0 and 1 can beset depending on the duration of the respective calls and theirrelationship to the time monitor thresholds.

Recommendation (Spatial Matrix Population)

Each entry in the spatial matrix is computed as a function of the one ormore of the various factors described above. More specifically, in oneimplementation, for the combination of an ith and jth subscriber, aentry M_(ij) in the spatial matrix can be computed to be equal to afunction of the speed factor for the ith and jth subscribers (s_(i) ands_(j), or s_(ij)) the dynamic range factor (DynRange_(ij)), thecorrelation factor (Correlation_(ij)), the frame error rates (FER_(i) &FER_(j)) for the respective subscribers, the alignment factor(Align_(ij)) and the monitor time (t_(i) and t_(j), or t_(ij))[Recommendation_(ij)=M_(ij)=f(s_(i), s_(j), DynRnage_(ij),Correlation_(ij), FER_(i), FER_(j), Align_(ij), and t_(ij)). Thefunction (f) can be a mathematical function or other construct forcombining the individual factors. In one implementation, each factor isweighted, with the sum of the weights being a fixed number (e.g., 1).

In one implementation, the recommendation (i.e., rating) is an 8-bitvalue. The value of 0 is assigned to entries where the monitoring timet_(ij) is insufficient. The value of 1 can be assigned to entries thatdo not exceed a minimum threshold for every factor. A value of 255 canbe assigned to entries that exceed a desirable threshold for everyfactor. Intermediate values can be assigned based on compliance with oneor more intermediate thresholds for each factor. For example, eachfactor may include three thresholds: the first threshold may be set at alevel that reflects an desirable value, a second threshold may be set ata minimal value, a third intermediary threshold may be set an acceptablevalue. The recommendation value can then be set depending on the numberof factors that exceed each threshold level. For example, anintermediate value of 128 can be assigned if all factors exceed theirrespective intermediary thresholds.

The recommendation can also be modified to include a best grouping orpairing. In some situations, no pairing or combination of existingsubscribers will be desirable or even rise to the level of acceptable.Even so, pairings or combinations may be made (e.g., when the riskassociated with the potential failed call is outweighed by the benefitsto making the combination). In this example, thresholds for each factormay be reset to lower levels and the recommendation process can berepeated. Alternatively, the system may provide a best combination basedon the empirical data (of the possible groupings) when no combinationsare acceptable.

Channel Assignment

Referring now to FIG. 2, a method for assigning channels 200 is shown.The method can include spatial channels where two subscribers share aspatial channel. Those of ordinary skill in the art will recognize thatother groupings (i.e., other than pairings) can be made. The methodincludes a check to determine if a request from a new subscriber hasbeen received (202). If not, a check is made to determine if a timeouthas expired, indicating that an optimal pairing analysis should beinvoked (204). If the timeout has not expired, then the processcontinues at step 202.

If a request from a new subscriber has been received at step 202, then acheck is made to determine if any conventional channels are available(206). If one is available, then the new subscriber is assigned to anavailable channel (208) and the process continues at step 202. If thereare no available conventional channels at step 206, then the spatialmatrix is retrieved and evaluated to determine a best pairing forexisting subscribers (210). In one implementation, the best pairing isdetermined to be the pairing corresponding to the entry in the matrixhaving a greatest value. When the best pairing is determined, one of thesubscribers of the best pairing is ordered to change channel assignmentsto the channel associated with the other of the best pairing (212).Concurrently, the new subscriber is assigned to the vacated conventionalchannel previously occupied by the transferred one of the subscribers ofthe best pairing (214). Thereafter the process continues at step 202.

If the timeout period in step 204 has expired (indicating that the timefor pairing analysis has arrived), then a check is made to determine ifone or more subscribers share a conventional channel (220). If nosubscribers share a channel, then the timeout timer is reset and theprocess continues at step 202. If subscribers share a conventionalchannel, then a first/next pair of subscribers that share a conventionalchannel are evaluated (222). If the evaluation indicates that thepairing is the best available pairing (224), then the process continuesby identifying (226) and evaluating (222) the next pair of subscribersthat share a conventional channel. If no more pairs are identified, thetimeout timer is reset and the process continues at step 202.

If the evaluation indicates that a better pairing is available in step224, then the currently identified pairing is separated (i.e., theexisting subscribers are reassigned to create a best pairing) and newassignments that can include new pairings are formed as appropriate(228). Thereafter the process continues at step 226. In oneimplementation, hysteresis is included in this process. Due to the risksassociated with moving calls and the potential interferences anddegradation that can result, continuous movement of calls isundesirable. To limit excess motion, the recommendation can includebuilt in hysteresis. That is, the recommendation provided by the spatialmatrix can be revised or processed in light of the level of improvementthat can be achieved. For example, a recommendation to move a call canbe made only when a potential pair is predetermined amount (e.g.,significantly) better than a current pair.

In one implementation, the evaluation of a pair described above in step222 includes the recognition of an available conventional channel. Aconventional channel may become free as another call is terminated.Accordingly, the sharing process optimally may separate a shared channeland reassign a subscriber to a newly freed (i.e., vacated) conventionalchannel. Which channel to move can be determined based on callcharacteristics of the two subscribers. Conventionally, the worst callof the two subscribers is moved. The worst call can be determined byanalysis of the degradation of the calls over time by looking atrecently stored FER and RSSI information. If more than one channel isshared, then the pair that is least optimal is separated. The spatialmatrix can be used to determine the least optimal pairing of the sharedchannels.

In one implementation, channel assignment may be augmented by the use ofa predicted quality channel assignment method. The predicted channelquality assignment method predicts the quality of a communication thatwill result from assigning a new connection to a particular conventionalchannel. This is can be accomplished by estimating the signal power andthe interference-plus-noise power that a subscriber will experience oneach conventional channel if assigned to that channel by using a modelof the RF environment and the SDMA processing, without actuallyassigning the call to any conventional channel. A method for predictingquality channel assignments is described in “CHANNEL ASSIGNMENT AND CALLADMISSION CONTROL FOR SPATIAL DIVISION MULTIPLE ACCESS COMMUNICATIONSYSTEMS.”

In one implementation, the method above is changed to include themovement of calls to ensure that one or more channels are free for a newcaller. In this implementation, a check is made to determine if apredetermined number of channels (e.g., 1) are available (i.e., have notbeen assigned to a call). If the predetermined number of channels is notavailable, then groupings (e.g., pairings) can be made using theinformation in the spatial matrix to free an appropriate amount ofchannels.

Call Preparation

Call processing includes providing specified performance at variouspoints of time during the life of a call. If a desired level ofperformance is not achieved, then call quality may suffer to the pointof dropping the call. When a call is established and while the call isup, there are a number of performance metrics (characteristics) that canbe measured. Associated with each metric may be one or morespecifications that define a performance level to be achieved. Examplesof metrics include those listed above including BER, FER, alignment, andthe like, as well as carrier sense, signal strength, alignment drift andabsolute alignment.

When making grouping decisions (i.e., to decide which calls to combinein a spatial channel), some or all of these metrics may be evaluated todetermine a best grouping as described above. However, the evaluation ofgroupings can be affected by changes made while processing the calls.Changes can arise due to performance issues, that is, the grouping canbe deemed to be better or worse than initially thought due to changes inthe performance of one or more of the terminal devices (e.g., handsets),the basestation or interferers.

In one implementation, after groupings are determined and stored in thespatial matrix, one or more performance enhancing activities can beinvoked. The performance enhancing activities can include activities tomake groupings that are identified as desirable, more desirable. Thatis, once a grouping (a “best” grouping) is identified as being one thatmay be required to be made (in the event a new call is received or achannel needs to be made available), one or more performance enhancingactivities can be invoked to make the potential grouping even moredesirable. For example, one or more metrics can be evaluated and changes(e.g., in alignment, frequency etc.) can be made for one or more of thecalls in the grouping. For example, the grouping may be a “best”grouping of those available, however, the grouping may itself still besub-optimal. Changes in the call specifications for members of thegrouping may result in a better performing group (in the event that thecalls are so grouped).

Alternatively, changes can be made to calls that are not included in the“best” grouping to enhance the success of a grouping should it arise.For example, calls not in the grouping can be shifted in frequency oralignment, resulting in a better performing best grouping.

The performance enhancing activities may be required to be performed atcertain times. For example, some changes may be required to be performedat the time of a slot switch (i.e., a TCH switch), while other changesmay be invoked immediately. Examples of performance enhancing activitiesare discussed in greater detail below. While alignment and frequencyshifts are discussed as possible performance enhancing activities, otherchanges may be invoked as is known in the art.

Performance Enhancing Activities

As discussed above, the transition to spatial channels can be risky.Characteristics of the calls (i.e., links) in a grouping can be changedbeforehand to minimize those risks. Furthermore, spatial channels mightnot function without certain link conditions and to attempt spatialchannels, these characteristics must be established ahead of time.

i. Alignment

Spatial processing algorithms may be sensitive to alignment amongcallers sharing a spatial channel. For some spatial processingalgorithms, the terminal units (e.g., handsets) must be at differentalignments to support spatial channels. In one implementation, the twoterminal devices must have an alignment difference of at least 1 symbolfor the spatial processing algorithms to successfully distinguish oneterminal unit from another. Other algorithms are more efficient if theterminal devices are on the same alignment. Still other systems mayperform better where each terminal device is shifted by some integerplus a half symbol. Accordingly, when a given grouping of calls (asidentified in the spatial matrix) may be realized, proactive alignmentchanges may be invoked depending on the performance criteria of thegiven spatial processing algorithms used.

Referring now to FIG. 3, a method for assigning channels 300 is shown.The method can include spatial channels where two or more subscribersshare a spatial channel. The method includes a check to determine if arequest from a new subscriber has been received (302). If not, a checkis made to determine if a timeout has expired, indicating that agrouping analysis should be invoked (304). If the timeout has notexpired, then the process continues at step 302.

If a request from a new subscriber has been received at step 302, then acheck is made to determine if any conventional channels are available(306). If one is available, then the new subscriber is assigned to anavailable channel (308) and the process continues at step 302. If thereare no available conventional channels at step 306, then the spatialmatrix is retrieved and evaluated to determine a best grouping forexisting subscribers (310). In one implementation, the best grouping isdetermined to be the grouping corresponding to the entry in the matrixhaving a greatest value. When the best grouping is determined, one ormore of the subscribers of the best grouping is ordered to changechannel assignments to the channel associated with one other of the bestgrouping (312). Concurrently, the new subscriber is assigned to thevacated channel previously occupied by the transferred one of thesubscribers of the best grouping (314). Thereafter the process continuesat step 302.

If the timeout period in step 304 has expired (indicating that the timefor grouping analysis and enhancement has arrived), then the spatialmatrix is updated (320). The updating can include the evaluation ofvarious characteristics of each subscriber (and link). Thereafter, thebasestation can invoke one or more enhancement activities to betterprepare the groupings for spatial channels (322). The enhancementactivities can include the shifting of frequency or alignment or otheractivities that are designed to better prepare the subscribers in agrouping for sharing a spatial channel as discussed in greater detailbelow. After the enhancement activities, a check can be made todetermine if a predetermined number of conventional channels areavailable in the system (324). In one implementation, no conventionalchannels are “reserved” for potential new subscribers. Alternatively,one or more conventional channels may be reserved. If the predeterminednumber of conventional channels is available, then the process continuesat step 302. If an insufficient number of conventional channels isavailable, then groupings of subscribers are performed (including movingcallers to appropriate spatial channels) using the spatial matrix untilthe predetermined number of conventional channels is available (326).The groupings may require the shifting of subscribers from oneconventional channel or from a spatial channel to another. Thereafterthe process continues at step 302.

The enhancement activities described above with respect to step 322 mayinclude alignment shifts in anticipation of grouping subscribers inspatial channels. As a practical matter, the uplink spatial algorithmson the basestation might not be able to keep up with the way in whichalignment changes. For example, when a terminal unit TCH switches andchanges alignment, the alignment of the terminal unit initially mighthave too much jitter to allow spatial algorithms to track the terminalunit. In one implementation, the alignment of the terminal unit isshifted prior to the TCH switch so that when the terminal unit TCHswitches into a spatial channel, its alignment will be more stable andthe spatial algorithm will be able to track well all of the groupedcalls sharing the spatial channel.

The terminal units themselves might not be able to track dramaticchanges in alignment. In one implementation, the spatial processingsystem requires one symbol difference between the terminal units toinitiate spatial channels. If the system tries to abruptly shift theterminal unit the entire one symbol as the system is attempting toestablish spatial channels, the terminal unit might drop the callbecause of an out-of-specification alignment shift. Accordingly, in oneimplementation, alignment shifts, where necessary, may be shifted ingradual increments to avoid the out-of-specification difficulties.

In one implementation, the alignment of all calls on the basestation isattempted to be shifted in a way such that any call could be paired withany other call in a spatial channel. The more calls processed, the moredifficult this task is to realize. The basestation may also be limitedby the absolute extent which alignments can be shifted (e.g., when theabsolute alignment shift limits for the system are within the range −1symbol to +1 symbol, it is impossible to shift four phonessimultaneously so that they all are shifted at least 1 symbol from eachother) or by the logistics by which the system shifts alignment (e.g.,if the basestation shifts solely through use of TCH switches, it wouldbe impossible to change alignment when all slots are full).

In one implementation, terminal units are prepared for spatial channelsas part of the enhancement activities of step 322. Each subscriber iscontinual monitored. In systems where shifting is accomplished using TCHswitches, at least one conventional channel must be available to supportenhancement activities (that way TCH switches can be used to shiftalignment). Information from the spatial matrix is evaluated todetermine a best pairing (grouping). A check is made to determine thealignment of each of the subscribers to the grouping. If the pairing(grouping of calls with the best characteristics for spatial channels)doesn't have the correct differential alignment, one of the two terminalunits associated with the subscribers is forced to TCH switch includinga forced change of alignment. Accordingly, when the time for filling thevacant slot arrives, the best candidates for spatial channels are readyto be grouped.

In another implementation, the best pairing may itself be a poor choicefor spatial channels. If the best available grouping is insufficient tosupport spatial channels, then one or more groupings of calls that areunsuitable for spatial processing may be identified. Members of thegroup may be forced to change alignment in the hopes that a new callercan be paired with one of the group and achieve an adequately performingspatial channel group. The system orders the terminal units associatedwith an “unsuitable” group are forced to TCH switch to the same (ordifferent, depending on the algorithms supported) alignment. When a newcall is received, the new call is forced to a different (the same)alignment than the members of the group. In this way, the new call willhave a greater chance of pairing with one call within the group.

In a system where call alignment can be drifted, then alignment changescan be forced as discussed above to enhance future groupings. In thesesystems, enhancement activities can be invoked without requiring a freeconventional channel. Calls are continually monitored and one or moregroupings of calls can be slowly drifted to alignments suitable forspatial channels. When a new call is received, the groupings will bebetter suited for spatial channels.

ii. Frequency

In a conventional system, shifting terminal units must pass a carriersense determination on a destination slot. During the period for testingby the shifting terminal unit, the two or more terminal units that areto occupy the slot to create a spatial channel have requirements thatare at odds. The shifting terminal unit performs a carrier sensedetermination by measuring background radiation on the destination slot,which must fall below a certain level if the switch is to be successful.At the same time, if the signal to the existing terminal units thatoccupy the slot drops to low for too long, the fer rate will exceed oneor more of the terminal unit's thresholds, causing the unit to request aTCH switch or a handover (i.e., causing a spatial channel to fail).

In one implementation, the shifting terminal unit can be enabled to passcarrier sense by stopping transmission on the slot all together for ashort period of time. Whether this succeeds or not depends on the lengthof time and the specifications of the particular model of the terminalunits using the slot. However, the original terminal units might notallow for loss of signal for the length of time needed for the shiftingterminal unit.

In another implementation, a method to pass carrier sense includes theuse of the spatial signature from the slot vacated by the shiftingterminal unit. The system can force the transmit weights one or moreterminal units (i.e., terminal units that are associated with a channelthat is too be shared) to be orthogonal to the spatial signature of ashifting terminal unit (i.e., the terminal unit that is to be shifted tothe shared channel). This solution should reduce the amount of powerdelivered to the shifting terminal unit enough that the basestationwould only need to reduce overall power transmitted rather thaneliminate it entirely (as proposed above). The shifting techniqueproposed is better suited to allow the system to stay within thespecifications of a broader range of terminal units.

Mathematically the weight being used to transmit to the initial terminaluser (the user transmitting originally on the channel that is to beshared) is defined as w_(i) and the spatial signature of the shiftinguser as s_(s). Then, the new weight used to transmit can be expressed as${w_{n} = {w_{i} - {s_{s}\frac{\left\langle {w_{i},s_{s}} \right\rangle}{{s_{s}}^{2}}}}};$

-   -   where <w_(i), s_(s)> is the standard complex dot product.

However, the spatial signatures and transmission weights differ atdifferent frequencies. Spatial signatures and weights also change overtime. Accordingly the origin slot and the destination slot must be ofthe same frequency or very close to the same frequency just before thesystem attempts to establish spatial channels.

In one implementation, the system forces all calls to be on the samefrequency. However, this solution may not be desirable because callquality may be affected due to interference on one of the slots at thecommon frequency.

Alternatively, only certain ones of the calls are kept at the samefrequency. In one implementation, terminal units are prepared forspatial channels as part of the enhancement activities described above.If a pair (grouping) of calls with the best characteristics for spatialchannels doesn't have the correct frequency, one of the two (or more)terminal units is forced to TCH switch including a forced change offrequency. Accordingly, when the vacant slot fills, the best candidatesfor spatial channels share the same frequency and are ready to begrouped.

The present invention has been described in terms of specificembodiments. The invention however, is not limited to these specificembodiments. Rather, the scope of the invention is defined by thefollowing claims and other embodiments are within the scope of theclaims.

For example, the present invention has been described in terms of aspecific wireless cellular communication system. Those of ordinary skillin the art will readily recognize the application of these principles toother similar communication systems, such as wireless local areanetworks.

The system has been described in terms of pairings of calls and a matrixof recommendations for pairings. A single channel may support more thantwo calls (N-calls) and as such a N-dimensional construct may be usedfor storing recommendation data for combinations of callers for a givenchannel (e.g., 3 callers sharing a channel and a three dimensionalstructure for storing information about combinations of triples (ofcallers)). In addition, the methods disclosed herein are applicable tosystems where spatial channels are used to support three or more callersand where callers are shifted to create larger groupings of callersdepending on demand (e.g., grouping three callers when all channelssupport two callers and a new channel is required to be freed).

The system has been described in terms of a pairing of existingsubscribers and the assignment of a new subscriber to a freeconventional channel. In one implementation, if no acceptable pairing ofexisting subscribers can be made, then a best pairing of the newsubscriber and an existing subscriber can be made. If no acceptablepairing can be located, then the new subscriber may not be serviced. Inone implementation, the new subscriber is evaluated along with othersubscribers to determine optimal pairings, however, the new subscribersfactors may be weighted based on the amount of data collected (e.g., thetime of call duration).

The system has been described in terms of a pairing of existingsubscribers and the assignment of a new subscriber to a freeconventional channel. In one implementation, the system includes pluralsubscribers on each of one or more spatial channels. In oneimplementation, the system does not free up a conventional channel forthe new subscriber. Alternatively, the system creates groupings ofsubscribers to create at least one “less populated” channel and a newsubscriber is combined with any existing subscribers on the lesspopulated channel. For example, if four spatial channels are available,each supporting two subscribers, the system would create the followinggroupings to support a new subscriber: one combination of threesubscribers from all the existing subscribers, two combinations of twosubscribers, and one less populated channel with but a singlesubscriber. When a new subscriber request is received, the newsubscriber is assigned to the less populated channel. In thisimplementation, the system determines a loading threshold for eachchannel including a maximum number of subscribers that can be assignedto a given channel. Assuming that the network loading threshold is notexceeded, the system creates groupings that allow for new subscribers tobe added while minimizing the performance hit from the added subscriber.If the network loading threshold will be exceeded, the new subscriber isnot supported (i.e., dropped).

Other variations will become evident from the descriptions providedwithout departing from the spirit and scope of the invention whichshould only be limited as set forth in the claims that follow.

1. A method comprising: forming potential combinations of existing radiocommunication system subscribers with conventional radio channels of astation of the radio communication system, at least some of thecombinations including more than one subscriber per conventional channelof the station with each subscriber having a unique spatial channel onthe same conventional channel; rating each potential combination;storing the ratings; and reassigning an existing subscriber to adifferent spatial channel based on the ratings.
 2. The method of claim1, further comprising performing an enhancing activity on the potentialcombinations to improve a rating for a potential combination such that apotential combination is better suited for spatial channels than anexisting combination.
 3. The method of claim 2, wherein performing anenhancing activity comprises changing an alignment of one or moreexisting subscribers in a combination.
 4. The method of claim 2, whereinperforming an enhancing activity comprises changing transmit weights ofa spatial signature for a subscriber in an existing combination to beorthogonal to transmit weights of a spatial signature of anothersubscriber in the combination.
 5. The method of claim 1, whereinreassigning existing subscribers comprises reassigning existingsubscribers prior to assigning a spatial channel to a new subscriber. 6.The method of claim 5, wherein reassigning existing subscriberscomprises freeing a conventional channel for use by the new subscriber.7. The method of claim 1, wherein reassigning existing subscriberscomprises reassigning an existing subscriber to a different frequency sothat the existing subscribers are separated by a predetermined frequencydifferential.
 8. The method of claim 7, further comprising determiningan optimal frequency differential for subscribers that share a spatialchannel and wherein reassigning an existing subscriber comprisesreassigning existing subscribers to an appropriate frequency inaccordance with the determined optimal frequency differential.
 9. Themethod of claim 1, wherein reassigning an existing subscriber compriseschanging a frequency for a plurality of subscribers to form a group ofsubscribers having an identical frequency such that a new subscriberhaving a different frequency can be paired with one or more of the groupto form a spatial channel.
 10. The method of claim 1, furthercomprising: determining if a potential combination of subscribers doesnot satisfy a performance criteria and as such the combination is not agood candidate for spatial channels, determining if an enhancingactivity may be applied to the potential combination to create apotential combination that satisfies the first performance criteria. 11.The method of claim 10, wherein the performance criteria is an alignmentcriteria for each subscriber assigned to a spatial channel.
 12. Themethod of claim 10, wherein the performance criteria is a frequencycriteria for each subscriber assigned to a spatial channel.
 13. Themethod of claim 10, wherein the performance criteria is selected fromthe group comprising, bit error rate, frame error rate, alignment, speedfactor, dynamic range factor, correlation factor and relative signalstrength factor.
 14. The method of claim 1, further comprising:determining a network loading threshold for the station for conventionalchannels including determining a number of conventional channels to beshared concurrently by subscribers as spatial channels at the stationand the number of subscribers to share each conventional channel; andwherein reassigning an existing subscriber comprises reassigning anexisting subscriber without violating the network loading threshold forthe station.
 15. The method of claim 14, wherein reassigning theexisting subscribers comprises creating one or more spatial channels andthereby freeing space on at least one conventional channel for a futuresubscriber.
 16. The method of claim 15, further comprising: receiving arequest to add a new subscriber; determining if the network loadingthreshold would be exceeded by adding the new subscriber; and if not,then adding the new subscriber to the at least one conventional channelon which space has been freed.
 17. The method of claim 1, furthercomprising receiving a request to add a new subscriber and whereinreassigning an existing subscriber is in response to receiving therequest.
 18. A machine-readable medium comprising data that whenoperated on by the machine cause the machine to perform operationscomprising: forming potential combinations of existing radiocommunication system subscribers with conventional radio channels of astation of the radio communication system, at least some of thecombinations including more than one subscriber per conventional channelof the station with each subscriber having a unique spatial channel onthe same conventional channel; rating each potential combination;storing the ratings; and reassigning an existing subscriber to adifferent spatial channel based on the ratings.
 19. The medium of claim18, wherein the operations further comprise performing an enhancingactivity on the potential combinations to improve a rating for apotential combination such that a potential combination is better suitedfor spatial channels than an existing combination.
 20. The medium ofclaim 18, wherein reassigning existing subscribers comprises reassigningexisting subscribers to free a conventional channel for use by a newsubscriber.
 21. A radio station comprising: multichannel transmitters tocommunicate with more than one radio communication system subscriber ona conventional channel using a unique spatial channel for eachsubscriber on the same conventional channel; a processor to formpotential combinations of existing subscribers with conventional radiochannels, to rate each potential combination, to store the ratings, andto reassign an existing subscriber to a different spatial channel basedon the ratings.
 22. The station of claim 21, wherein reassigningexisting subscribers comprises reassigning an existing subscriber to adifferent frequency so that the existing subscribers are separated by apredetermined frequency differential.
 23. The station of claim 21,wherein the processor is further to determine a network loadingthreshold for the station for conventional channels includingdetermining a number of conventional channels to be shared concurrentlyby subscribers as spatial channels at the station and the number ofsubscribers to share each conventional channel; and wherein reassigningan existing subscriber comprises reassigning an existing subscriberwithout violating the network loading threshold for the station.